The present invention relates to a distributed type delay line particularly adapted for use in a television receiver.
In general, a delay line is provided in a video amplifier in a television receiver in order to equalize the time delay for the luminance and chrominance circuits before the signals are combined in the matrix. Of various conventional distributed type delay lines, some typical examples will be described with reference to FIGS. 1 through 5. A delay line shown in FIG. 1 comprises a bobbin with a plurality of axially spaced coaxial flanges 1 defining a plurality of winding slots 2 therebetween, an electrode 4 formed on the surface of the bobbin 3 by applying an electrically conductive material and series-connected windings 5 of insulated wire. The equivalent circuit of the delay line shown in FIG. 1 is shown in FIG. 2. Inductance L is obtained from each winding 5 and capacitance C is induced between the electrode 4 and each winding 5.
The delay line of the type shown in FIGS. 1 and 2 has some defects. Firstly, coating of the electrode 4 is extremely difficult. The better the conductivity of the electrode 4, the greater the eddy current loss becomes. On the other hand, when the electrode 4 with relatively poor conductivity is used, the ground resistance is difficult in each slot 2 and the malconduction through the electrode 4 itself occurs. As a result the delay line characteristics are adversely affected. In addition, it is also extremely difficult to apply the wire with a uniform insulation coating. Therefore, due to the surface flaws such as pin holes and deterioration in insulation the shortcircuit between the electrode 4 and the windings 5 tends to occur. Furthermore, when an electrode forming material is applied on a burr left on the bobbin 3, a cutting-edge shaped projection is formed, breaking the insulation coating on the conductor. These phenomana are more common especially when the delay line is subjected to the temperature change.
Inductance L produced by each winding 5 frequently tends to be affected by the external noise from transistors in a video circuit, a flyback transformer and deflection yokes. Therefore, depending upon the position of the delay line in the color television receiver, shielding means must be provided.
Another example of the prior art delay lines is shown in FIG. 3. It consists of a bobbin 3 with axially spaced coaxial flanges 1 defining a coil slot 2 therebetween, coils 6 of insulated wire 5 and capacitor coils 7' each consisting of a bifilar winding of insulated wires 5 and 7, the coils 6 and 7 being alternately wound on the bobbin 3. FIGS. 4 and 5 show the electric and equivalent circuits, respectively. Each coil 6 induces inductance L while each coil 7' of the bifilar winding, capacitance C.
This delay line has also some defects to be described below. Firstly, the bifilar winding is such that it is difficult to obtain the bifilar windings with uniform quality. Furthermore, one end of each coil 7' must be connected to a ground terminal 8. In practice, each delay line is generally provided with 8 to 15 coils 7' and accordingly 8 to 15 connections to the terminal 8 must be made. Therefore, the delay lines of the type shown in FIG. 3 are not adapted for the mass production.
Moreover, the delay line tends to be adversely affected by the external noise so that shielding means must be provided depending upon the installation position.
A further defect is that each coil 7' has inductance L' which, together with capacitance C, makes up a filter circuit which disadvantageously attenuates the frequency characteristic of the delay line.